An integrated circuit package generally includes an integrated circuit having an active face lying on a chip support pad connected to a leadframe and encapsulated by a substance, such as plastic, to protect the IC. The IC package is typically mounted to a printed circuit board. Reflow solder is one technique used to surface mount the IC package to a printed circuit board.
As the industry moves towards thinner (50 mils or thinner, for example) packages or a larger chip size for higher volumetric packaging on printed circuit boards, however, new packaging techniques are evolving. Two such techniques are the lead-on-chip technique and the chip-on-lead technique. In both the lead-on-chip technique and the chip-on-lead technique, a chip support pad is not used. A thinner package or one with a larger chip size results. However, a problem occurs when surface mounting a lead-on-chip device and a chip-on-lead device to a printed circuit board by reflow solder. The heat generated during reflow solder can enhance the state of thermal mismatch between the dissimilar materials in the IC package creating high stresses in the encapsulating material. Additionally, at reflow temperature (typically about 215 C. to 260 C.) any moisture that may have been absorbed by the the encapsulating material is converted to steam. The steam pressure can be such that it delaminates the surface of the IC and the surface of the encapsulating material. The loss of adhesion under such conditions causes a high stress concentration in the encapsulant at the corner of the IC. This often leads to package cracking. As the area of the IC increases, cracking of the IC package in lead-on-chip and chip-on-lead devices resulting from reflow solder increases.
It is an object of this invention to provide a semiconductor integrated circuit that reduces cracking in a lead-on-chip and a chip-on lead package.
It is a further object of this invention to provide a lead-on-chip and a chip-on lead IC package that is resistant to cracking.
A further object of this invention is to provide a method of reducing cracking in a lead-on-chip and a chip-on-lead IC package.
Other objects and benefits of this invention will be apparent to those skilled in the art, based upon the description to follow herein.